Heavy duty diesel engines require crankcase lubricant oils which contain additives to stabilize oxidation, and which are non-corrosive to bearing materials including silver. Oxidation deterioration is undesirable because it can lead to decomposition of the engine lubricant. This deterioration of the lubricant has ramifications such as an increase in viscosity, the formation of sludge, and an increase in engine deposits. As the lubricant oxidizes it becomes more acidic and can cause corrosion of an engines' metal components such as bearing materials. In addition to utilizing additives to control oxidation, sludge, etc., care must be taken to ensure the additives themselves are not corrosive to metal components during engine operation.
Medium speed diesel engines are special because a significant number of railway diesel engines operated in the United States and other countries contain silver or silver surfaced bearing components. This poses a peculiar problem since many of the bearing protection additives which are effective at protecting other metal bearing surfaces, e.g. copper-lead, bronze, aluminium, are ineffective for protecting silver bearing components. In the case of materials such as zinc dithiophosphates, they are very corrosive to silver or silver-plated bearings.
Relatively high alkalinity in the lubricating oil is required to neutralize acids formed during the combustion process. However, some additives which contribute to high alkalinity, e.g., over-based phenates or sulfonates, are aggressive toward silver. This aggressive nature can result in excessive corrosion or wear of the silver-containing components of the engine. Therefore, a unique silver lubricity agent for medium speed diesel engines is needed as part of an intricate balance of additives to protect against the undesirable effects of lubricating oils on silver bearings.
A number of patents have disclosed lubricating oil compositions for silver protection, but none have provided the enhanced protection observed with the lubricating oil composition of the present invention.
U.S. Pat. No. 5,302,304 discloses a silver protective lubricant composition for an internal combustion engine, which contains the reaction product of an amine, formic acid, and a C5 to C60 carboxylic acid, a dispersant, metal detergent, and 0.01-1 wt. % of an organo-sulphur compound selected from sulphurised olefins, fatty acids or esters, sulphur-containing heterocyclic compounds, sulphurised hydroxy-aromatic compounds, disulphides, dithiocarbamates and thiadiazoles.
U.S. Pat. No. 5,244,591 discloses a lubricating oil composition for silver bearings wear reduction in internal combustion engine, which contains unsaturated carboxylic acid and no more than 0.08% wt sulfurized olefinic corrosion inhibitor. The sulfurized olefin comprises cosulfurized alkenyl ester-/alpha-olefin.
U.S. Pat. No. 4,734,211 discloses a lubricating oil composition for railway diesel engines which comprises a base oil, an ashless dispersant, an overbased alkaline earth metal akylphenolate, an alkaline earth metal alkyl sulfonate, an overbased alkaline earth metal phenolate, a polyhydroxy compound of up to 60 carbon atoms or a mixture, and a chlorinated hydrocarbon. The polyhydroxy compound comprises glycerol monooleate. The lubricating oil can reduce silver wear in marine and railway diesel engines.
U.S. Pat. No. 4,764,296 discloses a lubricating oil composition for railway diesel engines which comprises a base oil, an ashless dispersant, a mixture of overbased alkaline earth metal alkylphenolate and alkyl sulfonate compounds, a polyhydroxy compound of up to 60 carbon atoms or a mixture, and a chlorinated hydrocarbon. The polyhydroxy compound comprises glycerol monooleate. The lubricating oil can reduce silver wear in marine and railway diesel engines.
U.S. Pat. No. 4,495,088 discloses lubricating oil containing borated fatty acid esters of glycerol and a succinimide for internal combustion engine. Borated fatty acid ester of glycerol was found to be stabilized against hydrolysis in lubricating oil when used in conjunction with a succinimide compound. The borated fatty acid ester of glycerol is a mixture of borated glycerolmonooleate and glycerol dioleate. The combination of borated fatty acid ester of glycerol and succinimide has been found to reduce fuel consumption.
U.S. Pat. No. 8,071,515 discloses a lubricating oil composition for an internal combustion engine, in which a cylinder liner comprises cast iron or boron cast iron. The package comprises a baseoil, a fatty acid partial ester compound, an aliphatic amine compound and/or an acid amide compound, a benzotriazole derivative and a succinimide compound. The fatty acid partial ester could be a glycerol monooleate in 0.5-1.5% by mass based on the composition, and can react further with boron. The lubricating oil should have S<=0.3%, P<=0.12%, and SASH 1% based on the composition. The lubricating oil has enhanced friction reducing, oxidation stability and corrosion inhibiting effect.
U.S. Pat. No. 8,367,591 discloses a lubricating oil composition for an internal combustion engine. It contains sulfurated oxymolibdenum dithiocarbamate, acid amide, fatty acid partial ester/fatty-amine compound, and benzotriazole derivative. The fatty acid partial ester could be a borated glycerol monooleate in 0.3-0.6% by mass based on the composition. The lubricating oil has an excellent friction reducing and corrosion inhibiting effect for lead and copper.
US patent application number 20060111253 discloses a lubricating oil composition useful for crankcase internal combustion engine. It comprises base oil, ester of glycerol and higher carboxylic acid, and oil soluble molybdenum compound. The ester of glycerol and higher carboxylic acid could be a borated glycerol oleate. The lubricating oil has enhanced friction modification property.
US patent application number 20060276351 discloses an internal combustion engine lubrication package for improved fuel economy that comprises base oil, molybdenum salt, a borated epoxide, and monoester of polyol and aliphatic carboxylic acid. The monoester of polyol and aliphatic carboxylic acid comprises glycerol monooleate, and the borated epoxide has a specific structure with 300-1000 ppm boron to the composition.
U.S. Pat. No. 4,541,941 discloses a lubricating oil composition that comprises lubricating oil or grease, and a friction reducing amount of a borated mixture of a hydrocarbyl vicinal diol and hydroxyl-containing aliphatic carboxylate. The borated carboxylate could be borated glycerol monooleate.
Japanese patent application number 2010235851 discloses a lubricating oil composition for various applications. It contains base oil and a specific alkanoyl borate compound. The lubricating oil can achieve satisfactory wear resistance and oxidation stability, even when metal-free, phosphorus-free and sulfur-free additive are used.
U.S. Pat. No. 7,875,576 discloses a lubricating oil composition for internal combustion engine, which includes base oil, overbased detergent, oxymolybdenum complex, antioxidant, phosphorus compound and ester friction modifier. The ester friction modifier comprises borated glycerol monooleate.
U.S. Pat. No. 7,902,131 discloses a Mo-free and low P lubricating composition useful in engine oil that comprises base oil, diphnylamine compound, monoglyceride and/or ethoxylated amide and polyamine dispersant. The monoglyceride could be a borated epoxide or fatty epoxide.
Some of the patent art teach the use of sulfurized isobutylene in silver protecting lubricating formulation, and some teach the use of glycerol monooleate as silver lubricity agent. Although the use of borated glycerol monooleate as wear and/or corrosion inhibitors in internal combustion engines was mentioned in some art, none of the references teach borated glycerol monooleate as silver lubricity agent in railroad engine oil.
It is therefore desirable for crankcase lubricating oil compositions which protect silver bearings in medium speed diesel engines. It is also desirable for methods of lubricating medium speed diesel engines with crankcase lubricating oil compositions which protect silver bearings.